Exam 4 HWs (HW09, HW10, HW11)
Previous question. What happens to the size of the electrode A during the operation of the cell? There is no way to tell. it decreases it increases it doesn't change
it decreases
Cl2(g) + S2O32-(aq) ⟶⟶ Cl-(aq) + SO42-(aq) reducing agent? S2+ Cl2 S2O32- Cl
S2O32-
FeO (aq) + V2O5 (aq) → Fe2O3 (aq) + VO(aq) what is the reducing agent? V V2O5 FeO O Fe
FeO
How many moles of Cl2(g) are produced by the electrolysis of concentrated sodium chloride if 2.00 A are passed through the solution for 4.00 hours? The equation for this process (the "chloralkali" process) is given below. 2NaCl(aq) + 2H2O(l) ⟶ 2NaOH(aq) + H2(g) + Cl2(g) 0.149 mol 0.298 mol 0.00248 mol 0.0745 mol
0.149 mol
Calculate the cell potential for a cell based on the reaction below: Cu(s) + 2Ag+(aq) ⟶ Cu2+(aq) + 2Ag(s) when the concentrations are as follows: [Ag+] = 0.7 M [Cu2+] = 0.9 M (The temperature is 25°C and E° = 0.4624 V.) 0.459 V 0.455 V 0.470 V 0.447 V
0.455 V
Ca2+ (aq) + C(s) + ClO2 (g) → CaCO3(s) + ClO2- (aq) what is the total number of electrons transferred? 6 4 2 1
4
N2H4(g) + ClO3-(aq) ⟶⟶ NO(g) + Cl-(aq) The reaction takes place in basic solution. What is the smallest possible integer coefficient of ClO3- in the balanced equation? 1 2 3 4
4
Find the standard emf of the given cell diagram: Cu(s) | Cu2+(aq) || Au+(aq) | Au(s) Cu2+ + 2e- ⟶ Cu E° = +0.34 V Au+ + e- ⟶ Au E° = +1.69 V +1.35 V -1.35 V -2.03 V +2.03 V
+1.35 V
What should the voltmeter read? In previous questions +3.40 V +1.60 V +4.30 V +2.50 V
+1.60 V
A steel surface has been electroplated with 5.10g of vanadium (V, molar mass = 51 g/mol). If 2.90x104 C of charge were used, what was the original oxidation number of V? +3 +2 +1 +4
+3
Balance the following reaction in basic conditions and answer the following questions: Ca2+ (aq) + C(s) + ClO2 (g) → CaCO3(s) + ClO2- (aq) What is the oxidation state of C in CaCO3(s)? 0 -4 +4 +2 -2
+4
Consider the cell: Zn(s) | Zn2+(aq) || Cl-(aq) | AgCl(s) | Ag(s) Calculate E°. -1.20 V +0.54 V +0.98 V +1.20 V
+0.98 V Zn2+ + 2e- ⟶ Zn E° = -0.76 Ag+ + e- ⟶ Ag E° = +0.22 E°cell = 0.22-(-0.76) = 0.98 V
The equilibrium constant for the reaction below: 2Hg(l) + 2Cl-(aq) + Ni2+(aq) ⟶ Ni(s) + Hg2Cl2(s) is 5.6x10-20 at 25°C. Calculate the value of E°cell for this reaction. -1.14 V -0.57 V +1.14 V +0.57 V
-0.57 V
What would be the E° of an electrolytic cell made from the half-reactions below? AgCl(s) + e- ⟶ Ag(s) + Cl-(aq) E° = +0.22 V Al3+(aq) + 3e- ⟶ Al(s) E° = -1.66 V -1.88 -1.44 1.44 1.88
-1.88 ELECTROLYTIC CELL must have a (-) voltage
what is the largest approximate E° value that can be achieved when two half-cell reactions are combined to form a battery? 3 V 6 V -3 V -6 V
-6 V
Consider the cell: Zn(s) | Zn2+(aq) || Fe2+(aq) | Fe(s) If run at standard conditions, calculate the value of Δ𝐺∘𝑟𝑥𝑛 for the reaction that occurs when current is drawn from this cell. +62 kJ/mol -230 kJ/mol -31 kJ/mol -62 kJ/mol
-62 KJ/mol
What is Δ𝐺∘ for the half-reaction below? ClO3- + 6H+(aq) ⟶ 0.5Cl2(g) + 3H2O(l) E° = +1.47 194 kJ/mol -709,000 kJ/mol -709 kJ/mol 194,000 kJ/mol
-709 KJ/mol
Balance the following reaction in basic conditions: PbO2 (aq) + NO2- (aq) → Pb2+ (aq) + NO3- (aq) What is the coefficient of water? Is it a product or a reactant? 1, reactant 4, product 2 product 4, reactant 2, reactant 1, product
1, reactant
What is the ratio of [Co2+] / [Ni2+] when a battery built from the two half-reactions below reaches equilibrium? Ni2+ ⟶ Ni E° = -0.25 V Co2+ ⟶ Co E° = -0.28 V 3.20 10.33 0.31 0.10
10.33
2Fe2+ (aq) + H2O2 (aq) → 2Fe3+ (aq) + 2OH- (aq) how many electrons were transferred as it is balanced? 0 4 3 2 1 5 6
2
Cl2(g) + S2O32-(aq) ⟶⟶ Cl-(aq) + SO42-(aq) What is the smallest possible integer coefficient of SO42- in the combined balanced equation? 1 4 3 2
2
What is the E°cell for Zn(s) | Zn2+(aq) || Ce4+(aq) , Ce3+(aq) | Pt Zn2+ + 2e- ⟶ Zn E° = -0.76 Ce4+ + e- ⟶ Ce3+ E° = +1.61 0.85 V -2.37 V 1.61 V 2.37 V
2.37
What is the standard cell potential of the strongest battery that could be made using these half-reactions? Br2 + 2e- ⟶ 2Br- E° = +1.07 Fe3+ + 3e- ⟶ Fe E° = -0.04 Co3+ + e- ⟶ Co2+ E° = +1.80 Zn2+ + 2e- ⟶ Zn E° = -0.76 2.56 -2.56 1.84 1.11
2.56
Ca2+ (aq) + C(s) + ClO2 (g) → CaCO3(s) + ClO2- (aq) what is the coefficient on water? Is it a product or reactant? 3, reactant 1, product 3, product 6, reactant 1, reactant 6, product
3, product
FeO (aq) + V2O5 (aq) → Fe2O3 (aq) + VO(aq) what was the oxidation state of V in V2O5? 10 2 6 5
5
How long will it take to deposit 0.00235 moles of gold by the electrolysis of KAuCl4(aq) using a current of 0.214 amperes? 53.0 min 70.7 min 26.5 min 106 min
53.0 min
Balance the following reaction in acidic conditions and answer the next three questions: FeO (aq) + V2O5 (aq) → Fe2O3 (aq) + VO(aq) How many total electrons are transferred in this reaction? 5 3 6 2
6
Consider the cell reaction represented by the skeletal equation: Mn(s) + Ti2+(aq) ⟶ Mn2+(aq) + Ti(s) What is the proper shorthand notation for this reaction? A. Mn(s) | Mn2+(aq) || Ti2+(aq) | Ti(s) B. Ti(s) | Ti2+(aq) || Mn2+(aq) | Mn(s) C. Mn2+(aq) | Mn(s) || Ti(s) | Ti2+(aq) D. Ti2+(aq) | Ti(s) || Mn(s) | Mn2+(aq)
A
If E° for the disproportionation of Cu+(aq) to Cu2+(aq) and Cu(s) is +0.37 V at 25°C, calculate the equilibrium constant for the reaction. A. 1.8 x 10^6 B. 3.2 x 10^12 C. 2.4 x 10^2 D. 1.3 x 10^3
A
Standard reduction potentials are established by comparison to the potential of which half-reaction? A. 2H+ + 2e- ⟶ H2 B. 2H2O + 2e- ⟶ H2 + 2OH- C. Li+ + e- ⟶ Li D. F2 + 2e- ⟶ 2F-
A
The electrolysis of an aqueous sodium chloride solution using inert electrodes produces gaseous chlorine at one electrode. At the other electrode gaseous hydrogen is produced and the solution becomes basic around the electrode. What is the equation for the cathode half-reaction in the electrolytic cell? A. 2H2O + 2e- ⟶ H2 + 2OH- B. H2 + 2OH- ⟶2H2O + 2e- C. Cl2 + 2e- ⟶ 2Cl- D. 2Cl- ⟶ Cl2 + 2e-
A
What is the E° for the following electrochemical cell where Zn is the cathode? Fe | Fe2+ (1.0 M) || Zn2+ (1.0 M) | Zn E°(Zn) = -0.76, E°(Fe) = -0.44 A. -0.32 B. -1.20 C. +1.20 D. +0.32
A
Which species will oxidize Cr2+ (E°red = -0.407) but not Mn2+ (E°red = +1.224)? A. V3+ (E°red = -0.255) B. Zn2+ (E°red = -0.762) C. O3 in acid (E°red = +2.076) D. Fe2+ (E°red = -0.771) E. Pb4+ (E°red = +1.68)
A
Silver is plated on copper by immersing a piece of copper into a solution containing silver (I) ions. In the plating reaction, copper... A. is oxidized and is the reducing agent. B. is oxidized and is the oxidizing agent. C. is reduced and is the oxidizing agent. D. is reduced and is the reducing agent.
A This is a displacement reaction. The copper displaces the silver ions from solution, giving the reaction: Ag+ + Cu ⟶ Cu+ + Ag Copper loses electrons to form the ion, so copper is oxidized. Since copper gives electrons to silver, it cause silver to be reduced. Therefore, copper is oxidized and is the reducing agent.
A concentration cell consists of the same redox couples at the anode and the cathode and different concentrations of the ions in the respective compartments. Find the unknown concentration for the following cell: Pb(s) | Pb2+(aq, ?) || Pb2+(aq, 0.1 M) | Pb(s) E = 0.065 V A. 1.26 M B. 6.35 x 10^-4 M C. 15.8 M D. 7.97 x 10^-3 M
B
Cd(s) | CdSO4(aq) || Hg2SO4 | Hg(l) | Pt(s) What reaction occurs at the cathode? A. CdSO4(s) + 2e- ⟶2Cd(l) + SO42-(aq) B. Hg2SO4(s) + 2e- ⟶ 2Hg(l) + SO42-(aq) C. 2Hg(l) + SO42-(aq) ⟶Hg2SO4(s) + 2e- D. 2Cd(l) + SO42-(aq) ⟶ CdSO4(s) + 2e-
B
Consider 3 electrolysis experiments: 1. One Faraday of electricity is passed through a solution of AgNO3. 2. Two Faradays of electricity are passed through a solution of Zn(NO3)2. 3. Three Faradays of electricity are passed through a solution of Bi(NO3)3. Which of the following statements is true? A. Equal masses of all three metals are produced. B. Equal numbers of moles of all three metals are produced. C. Twice as many moles of metallic zinc are produced than metallic silver. D. The reaction producing the smallest mass of metal is that of the silver solution.
B
The standard voltage of the cell: Ag(s) | AgBr(s) | Br-(aq) || Ag+(aq) | Ag(s) is +0.73 V at 25°C. Calculate the equilibrium constant for the cell reaction. A. 5.1 x 10^14 B. 2.2 x 10^12 C. 2.0 x 10^-15 D. 4.6 x 10^-13
B
What is the standard cell potential of a battery made from the half reactions below? 2H+ + 2e- ⟶ H2 E° = 0.00V O2 + 4H+ + 4e- ⟶ 2H2O E° = +1.23 V A. -2.46 B. 1.23 C. -1.23 D. 2.46
B
The standard potential of the cell: Pb(s) | PbSO4(s) | SO42-(aq) || Pb2+(aq) | Pb(s) is +0.23 V at 25°C. Calculate the equilibrium constant for the reaction of 1 M Pb2+(aq) with 1 M SO42-(aq). A. 8.0 x 10^17 B. 7.7 x 10^3 C. 6.0 x 10^7 D. 1.7 x 10^-8
C
Zinc (Anode), Copper (Cathode) In this electrochemical cell, what is the reduction half reaction? A. Zn2+(aq) + 2e- → Zn(s) B. Cu(s) → CU2+(aq) + 2e- C. Cu2+(aq) + 2e- → Cu(s) D. Zn(s) → Zn2+(aq) + 2e-
C
Consider the voltaic cell: Pt | Sn2+ (0.10 M), Sn4+ (0.0010 M) || Ag+ (0.010 M) | Ag Sn4+ + 2e- ⟶⟶ Sn2+ E° = +0.15 V Ag+ + 1e- ⟶⟶ Ag(s) E° = +0.80 V The electrons flow in the external circuit from... A. Ag to Pt B. Sn2+ to Ag+ C. Pt to Ag D. Sn to Ag
C Electrons flow between the electrodes specifically.
Which of the metals in the list below will react with 1M H2SO4 to produce hydrogen gas? Na+ + 1e- ⟶⟶ Na E° = -2.714 Cd2+ + 2e- ⟶⟶ Cd E° = -0.403 Pb2+ + 2e- ⟶⟶ Pb E° = -0.126 Cu2+ + 2e- ⟶⟶ Cu E° = +0.337 A. Na, Cd, Pb, and Cu B. Cu only C. Na, Cd, and Pb only D. Na and Cd only
C For H2SO4 to produce hydrogen gas, it must be reduced. 2H+ + 2e- ⟶⟶ H2 E° = 0.00 Therefore, the metals have to oxidize, or act as the anode. This process must be spontaneous (E°cell > 0). 𝐸𝑐𝑒𝑙𝑙=𝐸𝑐𝑎𝑡ℎ𝑜𝑑𝑒−𝐸𝑎𝑛𝑜𝑑𝑒=0.00−𝐸𝑚𝑒𝑡𝑎𝑙Ecell=Ecathode−Eanode=0.00−Emetal For Ecell to be positive, the E° of the metal reduction must be negative. As the reduction of copper has a positive E°, it is the only metal that will not spontaneously react with H2SO4 to make hydrogen gas.
If the table of standard reduction potentials is ordered with the strongest reducing agents at the top, how are the reduction potentials ordered (from top to bottom)? A. from most positive to most negative B. from most common to least common C. from most negative to most positive D. from most spontaneous to least spontaneous
C educing agents have positive (spontaneous) oxidation potentials and negative (non-spontaneous) reduction potentials. If the best reducing agents are at the top, then the top of the table will contain the most negative (least spontaneous) reduction potentials and the bottom of the table will contain the most positive (most spontaneous) reduction potentials.
In the decomposition of cobalt (II) chloride, what substance is being oxidized? CoCl2 (s) → Co (s) + Cl2 (g) Cl Co CoCl2
Cl
Consider the cell diagram below: Mg(s) | Mg2+(aq) || Au+(aq) | Au(s) Mg2+ + 2e- ⟶⟶ Mg E° = -2.36 Au+ + e- ⟶⟶ Au E° = +1.69 What is the cathode and what is the cell type? A. Mg(s); an electrolytic cell B. Au(s); an electrolytic cell C. Mg(s); a voltaic cell D. Au(s); a voltaic cell
D
In an electrolytic cell, the negative terminal is the (cathode/anode) and is the site of the (oxidation/reduction) half-reaction. A. cathode, oxidation B. anode, oxidation C. anode, reduction D. cathode, reduction
D
Sodium is produced by the electrolysis of molten sodium chloride. What are the products at the anode and cathode, respectively? A. Na(l) and O2(g) B. O2(g) and Na(l) C. Cl2(g) and Na2O(l) D. Cl2(g) and Na(l)
D
The galvanic cell below uses the standard half-cells Mg2+ | Mg and Zn2+ | Zn, and a salt bridge containing KCl(aq). Identify electrode A (has a (-) charge) and write the half-reaction that occurs in that compartment. A. Zn(s); Zn(s) ⟶ Zn2+(aq) + 2e- B. Zn(s); Zn2+(aq) + 2e- ⟶Zn(s) C. Mg(s); Mg2+(aq) + 2e- ⟶ Mg(s) D. Mg(s); Mg(s) ⟶ Mg2+(aq) + 2e-
D
In a galvanic cell... A. oxidation takes place at the cathode B. electrolytes are added to carry electrons between electrodes C. electrical energy is used to reverse spontaneous chemical reactions D. oxidation and reduction take place at the same time, but at different electrodes
D The reaction in a galvanic cell is spontaneous and does not need to be driven by a battery. Both reduction and oxidation occur simultaneously, oxidation at the anode and reduction at the cathode.
Consider the half-reactions: Mn2+ + 2e- ⟶ Mn E° = -1.029 V Ga3+ + 3e- ⟶⟶ Ga E° = -0.560 V Fe2+ + 2e- ⟶⟶ Fe E° = -0.409 V Sn2+ + 2e- ⟶ Sn E° = -0.136 V Which of these redox couples could not be used to make a voltaic cell? A. Fe2+ + Mn ⟶ Mn2+ + Fe B. Sn2+ + Fe ⟶ Sn + Fe2+ C. 2Ga + 3Sn2+ ⟶ 2Ga3+ + 3Sn D. Sn2+ + Mn ⟶ Sn + Mn2+ E. 2Ga3+ + 3Fe ⟶ 2Ga + 3Fe2+
E Only 2Ga3+ + 3Fe ⟶ 2Ga + 3Fe2+ has a negative E°cell, so it is the only reaction here that is non-spontaneous.
If the standard potentials for the couples Cu2+|Cu, Ag+|Ag, and Fe2+|Fe are +0.34, +0.80, and -0.44 V respectively, which is the strongest reducing agent? Fe2+ Ag Ag+ Fe Cu Cu2+
F The best reducing agents are good oxidizers. Good oxidizers are bad reducers and, therefore, have low E°red. The pair with the lowest E°red is Fe2+|Fe. In this pair, Fe would oxidize to Fe2+. Therefore, Fe is the species that oxidizes and is the best reducing agent.
Which species is the weakest reducing agent in the table of half-reactions? F2 Li+ Li F-
F- For a molecule to be a weak reducing agent, it has to be a bad oxidizer/good reducer. The reduction of F2 to F- has the largest positive value on the table of standard reduction values. Therefore, its reduction is the most spontaneous and it would be the worst reducing agent. For it to work as a reducing agent, F- would have to oxidize into F2. Therefore, F- is the weakest reducing agent.
which species will REDUCE Ag+ but not Fe2+? K H2 Cr Co2+
H2 Ag+ + e- ⟶ Ag E° = +0.80 V Fe2+ + 2e- ⟶⟶ Fe E° = -0.44 V H2 has an E° of 0.00, and gives a positive E°cell when combined with Ag+ as the cathode but a negative E°cell when combined with Fe2+ as the cathode.
2Fe2+ (aq) + H2O2 (aq) → 2Fe3+ (aq) + 2OH- (aq) Which species is the oxidizing agent? O Fe3+ OH- H Fe2+ H2O2
H2O2
N2H4(g) + ClO3-(aq) ⟶⟶ NO(g) + Cl-(aq) reducing agent? NO Cl ClO3- N2H4
N2H4
For the reduction of Cu2+ by Zn, ΔG° = -212 kJ/mol and E° = +1.10 V. If the coefficients in the chemical equation for this reaction are multiplied by 2, ΔG° = -424 kJ/mol. Does this mean E° for the cell would be +2.20V? Not enough information is given. No. It is impossible to know without testing it empirically. Yes
No
PbS (s) + 2O2 (g) → SO2 (g) + PbO2 (s) oxidizing agent? PbS S Pb O O2
O2
In a working electrochemical cell (a galvanic cell or a battery), the cations in the salt bridge move toward the cathode. A. It is impossible to tell unless we know if the cathode is "+" or "-". B. It depends on the charge of the cation. C. True D. False
The cathode is ALWAYS the site of reduction. This means positive ions pick up electrons to become less positive. Therefore, the cathode is LOSING positive charge and cations (positively charged by definition) in the salt bridge will move towards the cathode to compensate.
You turn on a flashlight containing brand new NiCad batteries and keep it lit for a minute or two. Which of the following can be considered TRUE regarding the chemical state of these batteries? I. Δ𝐺 for the battery reaction is negative. II. Ecell > 0 III. The batteries are at equilibrium. IV. Ecell is substantially decreasing during this time. III only All are true. All but III I and II only All but IV
| and || only
